Prediction models for the dynamical behaviour of honeycomb gas seals

Honeycomb gas seals are used in high performance turbomachinery because their damping capabilities have a favourable stabilizing effect on the rotordynamics of the machine. The predictability of the dynamic behaviour of the seals is critical at design stage. Currently, an isothermal two-control-volume bulk-flow model is used simulate the dynamical behaviour of honeycomb gas seals. However, the effectiveness of this procedure is not always satisfactory. On the basis of new experimental data from the UHP test rig of GE Oil & Gas in Florence, new predictive models have been devised that take into account the thermal effects in the gas and alternative empirical relations for the friction. A versatile simulation tool has been developed to experiment the effect of new assumptions and speed up the formulation and verification cycle of new empirical correlations. As a result of this investigation, a striking insensitivity to all the attempted modifications has been acknowledged. A CFD analysis of the flow was judged useful at this point, to get a better understanding of the fluid dynamics at the scale of a honeycomb cell. A method was develop to conduct CFD simulations on a single cell, by exploiting the periodic geometry and the quasi-periodic properties of the flow. Fictitious source terms are used in the CFD simulation, based on a first order approximation of the slowly varying part of the flow.